Ever-increasing numbers of telephone customers may be coupled to local loop generation equipment, examples of which are security systems, doorbell answering devices, and access control mechanisms. In particular, doorbell answering systems are commonly utilized in multi-family housing units. These systems generally place a switching mechanism in series with the tip/ring lines running from the telephone company central office to the customer premises. Normally, this switching mechanism is closed, completing a circuit between the telephone company central office and the customer premises. In this closed state, customers are able to communicate voice and/or data over their telephone lines as if the access control system was not even present. However, this communication is subject to interruption at any time.
Consider the illustrative example of FIG. 1 where the local loop generation equipment is a doorbell answering system 105. Each of a plurality of customer premises is served by a pair of terminals on a first portion of an RJ71C terminal block 107. For the sake of convenience, FIG. 1 shows only one customer premises, although it is to be understood that, in practice, multiple customer premises would likely be present. A set of terminals on a second portion of the RJ71C terminal block 103 is used to provide connections to central office 101. Of course, the organization of the RJ71C terminal block into first and second portions is for purposes of illustration, as the terminal block could be organized in any of various ways, to be determined by the requirements of a given system design. Moreover, other types of terminal blocks could be used in place of the RJ71C if desired.
The set of terminals on the first portion of the RJ71C terminal block 107 are connected to a conventional tip-ring wire pair. This wire pair is routed to a given customer premises. A signal splitter 109 which provides a given customer premises with an analog voice communications port and a digital communications port may or may not be used. The analog voice communications port is connected to a telephonic device 111 such as a touch-tone phone, and the digital communications port is connected to a digital communications device such as an ADSL modem 113. In the present example, the digital communications port is adapted to implement the ADSL (asymmetric digital subscriber loop) standard.
When a visitor wishes to notify a person at a selected customer premises of his or her presence, the visitor presses one or more keys on a keypad of intercom telephone 115. The doorbell answering system 105 responds to the key presses by opening up the circuit between the first portion of the RJ71C terminal block 107 and the central office 101, effectively disconnecting the telephone 111 and the ADSL modem 113 from the central office 101. At this time, the doorbell answering system provides a local loop between the visitor at intercom telephone 115 and the first portion of the RJ71C terminal block 107 routed to the selected customer premises.
This open circuit is something of a nuisance if it interrupts a voice call already in progress. However, the open circuit is more problematic in cases where the transfer of data is interrupted. In the present example, once the circuit between the central office 101 and the ADSL modem 113 is broken, the modem will disconnect from the telephone line routed to the first portion of the RJ71C terminal block 107. The subscriber loses data during this interruption, and may also be faced with the inconvenience of having to re-log into an online service.
As stated above, the circuit between the central office 101 and the customer is broken so that a local loop may be provided between the customer premises and the intercom telephone 115. After the circuit has been broken, the door answering system then feeds a ringing signal to the telephone line routed from the first portion of the RJ71C terminal block 107 to the subscriber's premises. When a person at the customer premises takes telephone 111 off-hook, voice communications are now enabled between this person and intercom telephone 115. If this person wishes to grant the visitor access, this person presses a specified DTMF tone sequence on the telephone keypad of telephone 111 or, alternatively, presses a lock release button separate and apart from the telephone system to grant the visitor access.
Although the foregoing example deals with local loop generation equipment in the form of a doorbell answering system, other types of local loop generation equipment present similar problems. Whenever the local loop generation equipment creates a local loop, digital communications between the customer and the central office are interrupted.